PHP Error Array to string conversion -> Implode array to string

I would like to get the infos from a post_meta in wordpress, I receive datas from a form most of the fields are good execpt the array one which it gives me this error :

Warning: Array to string conversion line 140

the line :

$value = get_post_meta($postid, "nature_handicap", true)

what i’ve tried :

Nature du handicap * : <br><br>
';
$value = get_post_meta($postid, "nature_handicap", true);
if (is_array($value)) {
    $value = implode(",", $value);
}

 '
<br><br>

I ve tried to implode the array to a string, I was expectiong to receive my array as a string split with some comas